The present invention relates to methods for providing product consistency for particulate materials.
In general, products of the chemical industry fall into one of two types—formulaic chemicals and performance chemicals. Formulaic chemicals are defined by their composition. If they are sold in different grades, the grades are distinguished by the concentration of impurities. Examples include ammonia, benzene, carbon tetrachloride, diethyl ether, and formaldehyde. Performance chemicals, which include polymers, dyes, pigments, and fragrances, are valued because of what they do, not what their composition is. Important types of performance chemicals include fine particle products such as carbon black, silica, titania, tantalum, calcium carbonate which are used in applications including reinforcement, rheology, color, and conductivity.
In order to insure consistency, specifications are set for fine particle products. Typically these specifications will include one or more measures of morphology and may further include one or more measures of chemical constituents. Common measures of morphology are particle size, surface area, structure, porosity, aggregate size, and aggregate shape. Common measures of chemistry include bulk and surface composition as well as analyses of extractable species. Measurements of variability of these properties can be made either during manufacturing to insure the process remains in control (often referred to as quality control, or QC) or on the product prior to shipment (often referred to as quality assurance, or QA).
For example, carbon black is typically sold with at least one morphological specification, which may be surface area, particle size, structure, and porosity. Performance tests, such as, for example, bound rubber or compound moisture absorption (CMA) tests may also be run, depending on the intended use for the carbon black.
Despite these quality control and quality assurance (QC/QA) efforts, it is not unusual for a customer to complain that a batch of product received did not perform as expected, despite being “within spec”. For example, variations in the rate of rubber cure, the appearance of white haze on molded rubber parts, low thixotropy in adhesives, and variations in plastic compounding times have all been traced back to lot-to-lot variations of carbon blacks even when each lot was within specification. This often results in the producer undertaking a thorough and costly study of the process and product and trying to make adjustments so that the product once again performs as expected.
Determining why a product did not perform as expected is inefficient and often both time consuming and expensive. It involves evaluation to assess why a problem has occurred rather than avoiding the problem in the first place. Many times, the producer will adjust manufacturing steps, not understanding the result but only in an attempt to change the product somehow to see a product difference. At times, this amounts to guess work.
Therefore, there is a need, especially in the particulate material industry, for methods in which product consistency can be routinely insured.